This invention relates to hollow metallic sealing rings of the so-called low-load self-energizing static kind as used for instance in pumps, motors and other apparatus to form leakproof seals between opposed, usually plane, parallel surfaces.
Conventional metallic sealing rings for this purpose are of `C` or `O` shaped radial cross-section but these have a major disadvantage in that they have a high spring rate and for many applications when the seal must have a large diameter the resultant compressive loads required are extremely high and not suited to the relatively weak flanges such as are used, for example, on aero engines.
Difficulties also arise when the gap to be sealed between surfaces or flanges is relatively large as happens with certain engines because of the need to cater for the manufacturing tolerances in assembly of the various parts of the engine which determine the relative position of the flanges. Further, this accumulated tolerance is compounded by differential expansion of the flanges both longitudinally and radially. There is therefore constant movement as the engine temperature varies from cold to hot and sealing contact points are not of constant diameter. The sealing ring must accordingly be sufficiently resilient to cope with large amounts of radial and axial expansion and contraction.
To this end, various forms of sealing ring which, in radial section, are of concertina or bellows-shaped profile have been proposed and comprise two outer limbs, intended to engage the surfaces or flanges to be seated connected by one or more contiguous loops. Typical examples of such metallic sealing rings are those which are disclosed in U.S. Pat. Nos. 3,575,432, 3,797,836 and 4,121,843. In each of those examples the outer limbs are of sinuous configuration with curved extremities which make line contact with the surfaces or flanges to be sealed.